The UCC3884 is a high performance current mode PWM controller intendedfor single ended switch mode power supplies. The chip implements a frequency foldback scheme that decreases the oscillator frequency as the output voltage falls below a programmed value. This technique decreases the average output current sourced into a low impedance load which can occur during an output short circuit or overload condition. Excessive short circuit current is more prevalent in high frequency converters where the propagation delay and switch turn-off time forces a minimum attainable duty cycle. An accurate volt-second clamp limits the duty cycle during line or load transient conditions which could otherwise saturate the transformer. The volt-second clamp may also be used with an external overvoltage protection circuit to handle fault conditions such as current sense disconnect or current transformer saturation.

The frequency foldback, volt-second clamp, cycle-by-cycle current limit, and overcurrent shutdown provide a rich set of protection features for use in peak current-mode pulse width modulators.

• Frequency Foldback Reduces Operating Frequency Under Fault Conditions
• Accurate Programmable Volt-Second Clamp
• Programmable Maximum Duty Cycle Clamp
• Oscillator Synchronization
• Overcurrent Protection
• Shutdown With Full Soft Start
• Wide Gain Bandwidth Amplifier (GBW > 2.5 MHz)
• Current Mode Operation
• Precision 5-V Reference